5 . A uniform electric field points to the left. A small metal ball charged to −2 mC hangs at a 30° angle
from a string of negligible mass, as shown above. The tension in the string is measured to be 0.1 N.
What is the magnitude of the electric field? (sin 30° = 0.50; cos 30° = 0.87; tan 30° = 0.58.)
(A) 25 N/C
(B) 50 N/C
(C) 2,500 N/C
(D) 5,000 N/C
(E) 10,000 N/C
6 . A thin semicircular conductor of radius R holds charge +Q . What is the magnitude and direction of
the electric field at the center of the circle?
(A) (B)
(C)
(D)
(E) The electric field is zero at the center.7 . Above an infinitely large plane carrying charge density σ, the electric field points up and is equal to
σ/2ε (^) o . What is the magnitude and direction of the electric field below the plane?
(A) σ/2ε (^) o , down
(B) σ/2ε (^) o , up
(C) σ/ε (^) o , down
(D) σ/ε (^) o , up
(E) zero